Recently, display devices for electrically controlling the position of a movable shutter to display an image (hereinafter, referred to as “movable shutter-system display devices” has been proposed. Such a movable shutter-system display device is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2008-197668.
In each of pixels of a conventionally proposed movable shutter-system display device, a movable shutter is located between a pair of electrodes, and the position of the movable shutter is electrically controlled by a voltage applied to the pair of electrodes, and thus an image is displayed.
In the case where, for example, one of the pair of electrodes has a voltage of GND and the other electrode has a voltage of Vdd, the movable shutter is moved toward the other electrode among the pair of electrodes. In the case where one of the pair of electrodes has a voltage of Vdd and the other electrode has a voltage of GND, the movable shutter is moved toward the one electrode among the pair of electrodes at high speed.
When, for example, the movable shutter is moved toward the other electrode among the pair of electrodes, backlight is transmitted to put the pixel into a lit state. When the movable shutter is moved toward the one electrode among the pair of electrodes, backlight is blocked to put the pixel into a non-lit state.
In a liquid crystal display panel or a plasma display panel, an image can be displayed in this manner.
In a conventionally proposed movable shutter-system display device, an electrical signal needs to be input to the movable shutter, and therefore the movable shutter includes an amorphous silicon film doped with impurities (hereinafter, referred to as an “n+a-Si film”).
When the n+a-Si film included in the movable shutter has a large residual stress, the n+a-Si film deforms a movable section of the movable shutter and prevents the movable shutter from being driven. Therefore, the movable shutter needs to include an n+a-Si film having a tensile stress, or in the case where the n+a-Si film has a compressive stress, the residual stress needs to be small.
An n+a-Si film having a compressive stress (Mpa) near “0” has both of a low sheet resistance value and a high sheet resistance value, and thus is unstable.
The movable shutter also acts as a contact layer for transmitting an electrical signal from the side of a substrate. If the contact layer is formed of an n+a-Si film having a high sheet resistance value, a high voltage is required to operate the movable section. Therefore, for the contact layer, an n+a-Si film having a low sheet resistance value is preferable.
The present invention made to solve the above-described problems of the conventional art has an object of providing a technology for forming a movable shutter of a movable shutter-system display device comprising an amorphous silicon film material which has a low residual stress and thus is stable.
The foregoing and other objects and novel features of the present invention will be made apparent by this specification and the attached drawings.